The present invention is generally directed to a method and system for selecting information sources for transmission over a single physical connection. More particularly the present invention is directed to a method for arbitrating amongst a plurality of competing information sources in a manner which promotes the transmission of high priority subunits of information without starving the channel's transmission of low priority subunits. Even more particularly, the present invention is directed to systems and methods for transmitting information in packet form while providing a mechanism for source selection and/or arbitration based on subpacket units of information. In particular, the arbiter of the present invention manages a plurality of source priorities during the transmission duration of a single packet.
In those situations in which a single physical connection, be it optical or electrical, exists between a number of information sources, there is a clear need to determine which one of the information sources is to be provided with current utilization of the physical connection. In situations in which all of the information sources have the same importance or priority for transmission, there are a number of possible methods that may be employed for arbitrating the use of the single channel. For example, with all information sources having the same priority, a round-robbin approach may be used with each source getting its turn in a predefined sequence. In another scheme useful in such cases, the information source may be selected at random. In yet another channel utilization method, the “arbiter” for source selection may be structured to pick the source that has been waiting the longest (Least Recently Used—LRU).
However, in situations where there is a priority associated with a plurality of information sources all of which are competing for utilization of the same single physical connection, certain problems can arise that are not present even when the information sources are divided most simply into just two priority classifications: high priority and low priority. For example, if high priority sources are always given priority, lower priority sources may experience undue delay and/or may in fact be completely closed out of the transmission process. This is a particularly annoying problem when information is transmitted in packets and it is further divided into packet subunits, also often referred to herein as “flits” since in these situations one is also concerned with the fact that some sources may have already initiated transmission. On the other hand, one does not want to preclude at least some transmission for the lower priority sources. In these circumstances, however, there is a very real problem in determining how to prevent higher priority sources from excessively dominating the usage of the connection while still allowing lower priority usage which should still be at least somewhat constrained so as to preserve, as much as possible, a contiguous flow for the higher priority information packets.